<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="../vue.js"></script>
</head>

<body>
  <div id="app">
    <h1>{{person.name}}--{{person.age}}</h1>
    <button @click="person.age++">改变年龄</button>
    <hr>
    <button @click="isHot = !isHot">改变天气</button>
    <h1>今天的天气真{{isHot?"热":"冷"}}</h1>
    <img :src="url" alt="">
  </div>
  <script>
    Vue.config.productionTip = false;

    const vm = new Vue({
      el: "#app",
      data() {
        return {
          isHot: true,
          url: "",
          person: {
            name: "laowang",
            age: 19
          }
        }
      },
      watch: {
        isHot: {
          // wacth默认只能监视某个属性的变化,并不能在初始化的时候就执行handler函数
          //可以配置immediate属性,让watch在初始化阶段就立即监视
          immediate: true,
          handler(newValue, oldValue) {
            console.log("handler", newValue, oldValue);

            this.url = newValue ? "./re.webp" : "./leng.gif"
          }
        },
        person: {
          //对一个对象或者数组监视的时候,内部发送改变并不能触发handler 需要开启深度监视
          deep: true,
          handler() {
            alert("你老了")
          }
        }
      }
    })
  </script>
</body>

</html>